1. Field of the Invention
The present invention relates to an optical device module, more particularly to an optical lens module.
2. Description of Related Art
In recent years, various kinds of display apparatuses have been widely utilized in daily life. The display apparatuses are, for example, liquid crystal displays (LCDs), plasma display panels (PDPs), projection apparatuses, and so on. The projection apparatuses may be used to largely magnify an image frame with its projection lens, and has gradually become one of the mainstream large-size displays. Generally speaking, if the image frame projected by the projection apparatus is larger, the border of each pixel area in the image frame will be more distinct and may be recognized, which results in an unnatural image frame and deteriorates the quality. For example, when a word appears in the image frame as shown in FIG. 1A, the distinct border of each pixel area may make the letters with jagged contour, which is uncomfortable to look at. In order to solve the above problem, in the conventional art, a reflective mirror capable of swinging back and forth is disposed on the light path of the image beam produced by an optical engine in the projection apparatus, such that the transmission direction of the image beam may be changed back and forth rapidly with a small angle. Therefore, the border of each pixel area will become blurred and unrecognizable, and thus the image frame is more natural and comfortable to look at. For example, referring to FIG. 1B, the blurred border of each pixel area makes the letters in the image frame become more smooth.
The aforementioned reflective mirror capable of swinging back and forth is usually disposed in a reflective mirror module. FIG. 2A is a schematic top view of a conventional reflective mirror module, and FIG. 2B is a cross-sectional view of the reflective mirror module in FIG. 2A taken along line A-A. Referring to FIGS. 2A and 2B, the conventional reflective mirror module 100 includes a foundation 110, a voice coil motor 120 (as shown in FIG. 2B), a lens base 130, a reflective mirror 140, and two shafts 150. The reflective mirror 140 is disposed on the lens base 130. One end of each shaft 150 is solidly connected to the lens base 130, and the other end is pivotally connected to the foundation 110 through a bearing (not shown). The voice coil motor 120 is disposed between one end of the lens base 130 and the bottom of the foundation 110. The top of the voice coil motor 120 is capable of vibrating up and down, so as to drive the lens base 130 to swing back and forth along the shafts 150.
In the conventional reflective mirror module 100, since the voice coil motor 120 is disposed below the lens base 130, the action moment arm and the action torque of the voice coil motor 120 are limited by the size of the lens base 130, and thus the swing speed and angle of the reflective mirror 140 are restricted, thereby restricting the improvement of the image frame. Besides, along with the miniaturization of electronic products, the lens base 130 is made smaller and smaller, so the design that the voice coil motor 120 is disposed below the lens base 130 becomes more difficult to make the reflective mirror 140 swing back and forth at a sufficient high speed and large angle. Moreover, the design that the voice coil motor 120 is disposed below the lens base 130 may restrict the reducing of the thickness of the reflective mirror module 100. Further, when the voice coil motor 120 is powered off, no appropriate external force is provided to make the lens base 130 stay at a specific position, so the reflective mirror module 100 needs an extra feedback control circuit to ensure the lens base 130 smoothly starts to swing from a static state, so as to avoid any collisions or noises in the voice coil motor 120 due to inappropriate application of force. Besides, the bearing in the reflective mirror module 100 easily fails due to abrasion, which may deteriorate the reliability of the reflective mirror module 100.